Seal ring

ABSTRACT

A plurality of first inclined faces ( 51 ) are provided on a side face of a seal ring ( 5 ) to be distanced away from each other. The first inclined face ( 51 ) opens to an inner circumferential face ( 23 ) and the side face of the seal ring ( 5 ). A column portion ( 54 ) is provided between adjacent first inclined faces ( 51 ). Portions at both ends of the first inclined face ( 51 ) serve as converging portions ( 52 ) that are conical smoothly-inclined faces, each converging to the adjacent column portion ( 54 ). On the column portion ( 54 ), the second inclined face ( 57 ) is formed.

This application is a 371 of international application PCT/JP2004/004792file Apr. 1, 2004, which claims priority based on Japanese patentapplication No. 2003-99310 filed Apr. 2, 2003 , which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seal ring, mounted in a ring grooveprovided in a shaft of a device such as an automatic transmission(hereinafter, simply referred to as AT), for maintaining the oilpressure required for an operation of that device.

2. Description of the Related Art

Seal rings used in a device such as an AT are respectively mounted in apair of ring grooves, provided on an outer circumferential surface(periphery) of a shaft of the device, to be distanced away from eachother. The outer circumferential surface of the seal ring is in contactwith an inner circumferential surface of a housing for accommodating aclutch plate or a brake plate slidable on that surface. Each of the sealrings receives operating (hydraulic) oil, supplied from an oil channelbetween the ring grooves, at one side face, i.e., a pressure-receivingside face, and the inner circumferential face thereof while sealing theside face of the ring groove and the inner circumferential surface ofthe housing with the opposite side face, i.e., the contact side face,and the outer circumferential surface. Sliding movement of the side faceof the seal ring, with respect to the wall face of the ring groove,maintains the operating oil at an appropriate pressure between the sealrings.

Under this condition, the seal ring is required to show small frictionalloss and to be able to maintain good sealing properties for a long time.When the seal ring is thus mounted, any frictional force between theside face of the seal ring and the wall face of the ring groove of theshaft has to be small. However, in the case of a conventional seal ringhaving a rectangular cross section, the contact area between the sideface of the seal ring and the wall face of the ring groove is large.Consequently the frictional loss is large.

In recent years, improvements in fuel consumption by further reducingthe weight of the AT and reduction of friction have been demanded fromthe viewpoints of improving vehicle performance and increasingly tighterenvironmental standards. Thus, for the seal ring, an improvement in itscharacteristics has been demanded so as to achieve both reduction infriction between the seal ring and the wall face of the ring groove andgood sealing properties irrespective of the processing accuracy of thering groove.

As an example of a typical conventional seal ring, JapaneseUtility-Model Laid-Open Publication No. Hei 6-18764 discloses a sealring, as shown in FIGS. 4 and 5. A seal ring 5′, mounted in a ringgroove 4 of a shaft 1, has an annular groove 22 on its side face thatextends in a circumferential direction, and a plurality of grooves 21that are distanced away from each other in the circumferential directionso as to be directed in a radial direction. Through the radiallydirected grooves 21, the annular groove 22 is opened to the innercircumferential face 23 of the seal ring 5′. The side face of the sealring 5′ is opposed to and in contact with the side face of the ringgroove 4 through the radially directed grooves 21 and the annular groove22. The reference numeral 2 denotes a housing, and 8 denotes a flow ofsupplied oil.

Japanese Patent Laid-Open Publication No. Hei 9-210211 discloses a sealring 5″ having a plurality of oil grooves 24 on the side faces of theseal ring 5″ to be distanced away from each other (the grooves 24 areopened toward the inner circumferential face of the seal ring 5″), andan inclined concave portion 24′ as a wedge-effect generation face thatextends at the circumferential direction side of that oil groove and isconnected to that oil groove.

In each of the above two seal rings 5′ and 5″, a pushing force againstthe wall face of the ring groove is reduced by the pressure from oilintroduced into the radially directed grooves 21, 24, thecircumferentially directed groove 22, and the concave portion. Thereforethe contact pressure between the seal ring and the wall face of the ringgroove is reduced. Thus, the above seal rings 5′ and 5″ are effective atreducing friction and improving lubricating function.

However, due to variation in the processing accuracy of the wall face ofthe ring groove, the ring groove often broadens outward, i.e., the wallface 7′ of the ring groove is often tapered in such a manner that thewidth of the ring groove at the bottom of the ring groove is smallerthan that at the opening thereof, as shown in FIG. 6. When the seal ringshown in FIG. 4 or 6 is used with such a ring groove, an innercircumferential corner of the side face of the seal ring may come intocontact with the wall face 7′ of the ring groove. This allows oil thatentered the region on the inner circumferential side of the seal ring toleak through gaps with the seal ring away from each other, resulting indegradation of the seal properties of the side face of the seal ring.

A seal ring for overcoming the above problem is described in JapanesePatent Laid-Open Publications Nos. Hei 8-219292 and Hei 9-217836. Asshown in FIG. 7, in this seal ring 5′″ a side face 57 is tapered at anangle of 2° to 10° in such a manner that the width of the seal ring onthe inner circumferential side is smaller than that on the outercircumferential side. For this seal ring 5′″, since the side face 57thereof is tapered, contact between the side face 57 and the wall face7′ of the ring groove does not disengage even if the ring groovebroadens outward because of variations in the processing accuracy of thewall face 7′. Thus, this seal ring 5′″ has an advantage in that thesealing properties are not significantly degraded.

Moreover, since the side face of the seal ring is a tapered face that isinclined inward as it travels radially inward, a wedge-like gap 56 thatis opened inward in the radial direction is formed between the side faceof the seal ring and the sidewall face of the ring groove. Thus, anycontact pressure between the seal ring 5′″ and the sidewall face of thering groove is reduced by the pressure from the oil introduced into thatgap 56. Friction is thus reduced.

However, in a case where the groove broadens outward because ofvariations in the processing accuracy of the wall face of the ringgroove, the above-described wedge-like gap is not formed between theside face of the seal ring and the side wall face of the ring groove.Thus, the above-described action of the oil pressure is inadequate andthe desired reduction of friction cannot be achieved.

FIG. 8 shows a seal ring 5″″ obtained by improving the above seal ringdescribed in Japanese Patent Laid-Open Publication No. Hei 8-219292. Theseal ring 5″″ is provided with a tapered face in such a manner that thewidth between both side faces of the seal ring on the innercircumferential side is smaller than that on the outer circumferentialside.

A feature of this seal ring 5″″ is as follows. Both the side faces areformed to be two-tier tapered faces each of which includes a firstinclined face 58 and a second inclined face 59 arranged on the innercircumferential side of the first inclined face 58. Here, theinclination angle of the second inclined face 59 is larger than that ofthe first inclined face 58. In this example, the inclination angle ofthe first inclined face 58 is set in the range from 0.5° to 3°, whilethe inclination angle of the second inclined face 59 is set in the rangefrom 9° to 11°.

This seal ring 5″″ has an advantage that, even if the wall face of thering groove is tapered like the wall face 7′ where the ring groovebroadens outward, contact between the side face of the seal ring 5″″ andthe sidewall face of the ring groove does not disengage. This is due tothe inclination angle of the first inclined face 58 positioned on theouter circumferential side. Therefore significant degradation of thesealing properties does not occur. Moreover, due to the inclinationangle of the second inclined face 59 positioned on the innercircumferential side, the contact pressure between the seal ring 5″″ andthe sidewall face of the ring groove is reduced by the action ofpressure from oil introduced into the gap 56. Friction is thus reduced.

However, in the seal ring having the one-tier tapered structure, an oilleakage path which releases inside oil pressure to the outside throughthe wedge-like gap is formed between a top end of a projection having anabutting end structure and an end face of the wall of the ring groovethat is opposed to the top end of the projection. Thus, the sealingeffect of this type of special abutting end structure cannot besufficiently maintained.

In addition, the principle of the seal ring having a two-tier taperedstructure is the same as the above seal ring of a one-tier taperedstructure. Thus, although the seal ring of the two-tier taperedstructure can improve sealing properties, there is still a problem withthe sealing properties that needs to be overcome.

SUMMARY OF THE INVENTION

The present invention was made in order to solve the problems that couldnot be overcome with the aforementioned conventional technologies, andit is an object of the present invention to provide a seal ring that canmaintain low friction and can reduce oil leakage without being affectedby processing accuracy of a sidewall face of a ring groove and dependingon an abutting end structure of the seal ring.

In order to achieve the above object, the present invention basicallyemploys a structure in which concave portions and flat column portionsas a framework of a body of a seal ring are alternately and continuouslyformed on a side face of the seal ring. The concave portion is formed bya deepest inclined portion (first inclined portion) and convergingportions positioned on both sides of the first inclined portion in acircumferential direction. The first inclined portion is provided in aninner circumferential part of the side face of the seal ring to reduce athickness of the seal ring toward the inner circumference of the sealring. Each of the converging portions converges to a point of theadjacent column portion that is the closest to the inner circumferenceof the seal ring. On the inner circumferential side of the columnportion and the converging portion, a second inclined portion isprovided so as to reduce the thickness of the seal ring toward the innercircumference of the seal ring.

In this structure, because of a wedge-like gap between the concaveportion of the side face of the seal ring and the sidewall face of thering groove, a force pushing the other side face of the seal ring can becanceled, thereby reducing loss torque generated between the side faceof the seal ring and the wall of the ring groove. Moreover, bychamfering the column portion to provide the second inclined face insuch a manner that the thickness of the seal ring is reduced toward theinner circumference of the seal ring, a contact position at which theseal ring comes into contact with the ring groove can be arranged outerin the radial direction as compared with a conventional seal ring, evenif the ring groove broadens outward.

Thus, an oil-pressure opening that releases inner oil pressure to theoutside can be made smaller, resulting in significant improvement insealing properties of the seal ring.

Furthermore, according to the seal ring of the present invention, anouter circumferential part of the side face is formed by a flat faceperpendicular to the outer circumferential face of the seal ring. Thus,the seal ring of the present invention can achieve excellent sealingproperties irrespective of a shape of an abutting end portion.

It is now described how the concave portion of the side face accordingto the present invention functions. The concave portion of the side faceof the seal ring, which is opposed to the annular ring groove of theshaft, is formed by the deepest inclined portion (first inclinedportion) and smooth converging portions arranged on both sides of thedeepest inclined portion in the circumferential direction. The deepestinclined portion is opened only toward the inner circumferential face ofthe seal ring side. The converging portions connect with the flatportion of the side face of the seal ring and serve as an inclinationface for generating wedge-effect. Thus, the wedge-like gap is generatedbetween the concave portion of the seal ring and the sidewall face ofthe ring groove, and cancels a force pushing the other side face of thering. As a result, loss torque generated between the side face of theseal ring and the groove wall can be surely reduced, thus improving fuelconsumption of a product using the seal ring of the present invention.

Moreover, in an abutting end portion, no concave portion is formed onthe side face. Instead, the abutting end portion is formed to be flat.Thus, an advantageous effect of the special abutting end structure canbe achieved sufficiently. Therefore, it is possible to ensure thesealing properties including low oil leakage property.

Furthermore, according to the present invention, a connecting portionbetween the column portion and the deepest portion of the concaveportion in the side face of the seal ring is formed by a conicalinclined face. Thus, it is possible to allow oil entering the concaveportion to be smoothly taken into a sliding face, i.e., the columnportion, so that the oil is supplied to the sliding face to improveabrasion resistance. In addition, due to the conical inclined face, thedirection of the lifting force becomes closer to a directionperpendicular to the rotating direction of the seal ring. Thus, acanceling pressure is further amplified by the addition of the liftingforce. Friction is thus reduced further. In addition, by optimizing thenumber of the concave portions and the number of the column portions,friction can be reduced more effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a seal device according to anembodiment of the present invention, showing a region where a seal ringis mounted.

FIG. 2 shows a partial Plan view of the seal ring according to theembodiment of the present invention as shown in FIG. 1 in which an innercircumferential surface is developed.

FIGS. 3( a) and 3(b) show cross-sectional views of the seal ring of thepresent invention, taken along line II-II and line III-III in FIG. 2,respectively.

FIG. 4 shows a cross-sectional view of a conventional seal device,showing a region where a seal ring having a groove on its side face ismounted.

FIG. 5 shows a partial plan view of the conventional seal ring shown inFIG. 4.

FIG. 6 shows a cross-sectional view of a conventional seal device,showing a region where a seal ring having an oil-groove on its side faceis mounted.

FIG. 7 shows a cross-sectional view of a conventional seal device,showing a region where a seal ring having a tapered side face ismounted.

FIG. 8 shows a cross-sectional view of a conventional seal device,showing a region where a seal ring having a two-tier side face, thatcorresponds to improved tapered side face, is mounted.

FIG. 9 shows a shape of a groove used in an example of the presentinvention.

FIG. 10 is a graph showing test results of the seal device of thepresent invention and the conventional seal device.

FIG. 11 shows an inner circumferential face of the seal ring accordingto an embodiment of the present invention and a component of cancelingpressure acting on a concave portion of the seal ring.

FIG. 12 is a graph showing a test result about a relationship betweenthe number of the concave portions of the seal ring of the presentinvention and friction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described based on the preferredembodiments, with reference to the drawings. FIG. 1 is a view in which aseal rings 5 of the present invention are mounted in each of a pair ofring grooves 4 that are provided on an outer circumferential surface ofa shaft 1 and distanced away from each other. A channel between the ringgrooves 4 delivers operating oil 8 to a pressure-receiving side face 9and an inner circumferential face 23 of each seal ring 5. Each seal ring5 forms a seal with sidewall face 7 of the ring groove 4 and the innercircumferential surface of a housing 2 by their proximity with contactside face 6 and outer circumferential face 55 respectively. In the innercircumferential part of each side face of the seal ring 5, concaveportions are formed.

As shown in FIG. 2, the concave portion is formed by the first inclinedface 51 and converging portions 52 arranged on both sides of the firstinclined face 51 in the circumferential direction. The convergingportion 52 converges to a point B in an adjacent column portion 54 whichis the closest point to the inner circumference of the seal ring 5. Theconcave portion has a pocket-like shape that extends long in thecircumferential direction.

The concave portion has a shape obtained by extending the deepestportion (first inclined face) 51 in the circumferential direction and ispositioned away from the other concave portions in the circumferentialdirection. Between the concave portions is provided a column portion 54in the form of a flat bank. On the inner circumferential side of thecolumn portion 54 and the converging portion 52, the second inclinedface 57 is formed in such a manner that the thickness of the seal ringis reduced toward the inner circumference of the seal ring 5.

As described above, the seal ring 5 of the present invention has thefeature that its side face includes concave portions and column portions54 continuously and alternately arranged in the circumferentialdirection.

It is preferable that the width of the first inclined face 51 in thecircumferential direction be larger than its maximum depth thereof andbe also larger than the width of the second inclined face 57 in thecircumferential direction. Please note that the width of the secondinclined face 57 in the circumferential direction is the width of thecolumn portion in the circumferential direction (the width betweenpoints B in FIG. 2). It is more preferable that the width of the firstinclined face 51 in the circumferential direction be 8-50 times as largeas the width of the second inclined face 57 in the circumferentialdirection. In a case where the width of the first inclined face 51 inthe circumferential direction is smaller than 8 times the width of thesecond inclined face 57 in the circumferential direction, experimentsdemonstrated that the contact area between the side face of the sealring and the wall face of the ring groove increased and thereforedecreased friction reducing effects. On the other hand, in a case wherethe width of the first inclined face 51 in the circumferential directionis larger than 50 times that of the second inclined face 57, the effectof a lifting force (detailed later) is small and friction is notmarkedly reduced.

Moreover, it is preferable that the width of each converging portion inthe circumferential direction be equal to or larger than 1/50 of thewidth of the first inclined face 51 in the circumferential direction. Ina case where the width of each converging portion in the circumferentialdirection is smaller than 1/50 of that of the first inclined face 51,the inclination of the converging portion becomes steeper. Thus, theeffect of the lifting force to be detailed later is small, and losses intorque are not markedly reduced. The width of the converging portion inthe circumferential direction has no upper limit. Even in a case wherethe concave portion does not include the first inclined face 51 but isformed by the converging portion only (in this case, the convergingportion extends from a point of contact with the column portion 54 tothe deepest inclined part of the concave portion and then convergestoward the inner circumferential side of the opposite column portionimmediately), advantageous effects of the present invention can beachieved. However, the friction reducing effects can be further improvedby providing the first inclined face 51. Especially, until a width ratioof the first inclined face to the converging portion reaches about 1 to1, friction is significantly decreased.

FIGS. 3( a) and 3(b) show cross-sectional views taken along line II-IIand line III-III in FIG. 2, respectively. As shown in FIG. 3( a), theinclination angle α of the first inclination face 51, forming theconcave portion in the side face of the seal ring, is measured withrespect to a plane perpendicular to the outer circumferential face 55 ofthe seal ring 5, i.e., a plane perpendicular to the axial center of theseal ring 5. This inclination angle α is preferably in the range from 8°to 45°, more preferably in the range from 14° to 18°. In a case of aconcave portion having no first inclination face, the inclination angleat the deepest inclined part of the concave portion is set within therange described above.

By setting the inclination angle α within the above-described range, alifting force has a direction made closer to a direction perpendicularto a rotating direction of the seal ring by a wedge-like gap 53 formedbetween the sidewall face of the ring groove and the concave portion ofthe seal ring, i.e., the first inclined face 51, and the conicalconverging portions 52 at both ends of the concave portion. This liftingforce act on oil and cancels a force pushing the other side face of theseal ring. Thus, there is a reduction in torque loss arising between theside face of the seal ring and the wall face of the ring groove, therebyresulting in an improvement in fuel consumption.

FIG. 11 shows the action of the lifting force. The canceling pressureacting on the first inclined face 51 also acts on the converging portion52. The lifting force is a part of this canceling pressure, i.e., acomponent force, and acts in the same direction as the canceling force.This lifting force contributes to the reduction of torque loss.

In a case where the inclination angle α of the first inclined face 51 issmaller than 8°, the wedge-like gap 53 that opens radially inward cannotreadily form between the side face of the seal ring and the sidewallface of the ring groove. Thus, any friction reducing effects areinsufficient. Moreover, in a case where the inclination angle α islarger than 45°, the wedge-like gap 53 is not formed and therefore thecanceling pressure is not generated. Thus, friction cannot be reducedsufficiently.

The outermost point of the first inclined face 51 in the radialdirection of the seal ring is arranged at a distance L from the outercircumferential face 55 of the seal ring in the radial direction. It ispreferable that L be in the range from 0.4 mm to 1.2 mm or be equal toor smaller than ⅔ of the dimension a1, shown in FIG. 3( a).

A portion having a width of L between the outer circumferential face 55and the outermost point of the first inclined face 51 in the radialdirection is a flat portion and is preferably formed intermittently. Ina case where L is smaller than 0.4 mm, it is likely that the outermostpoint of the concave portion of the seal ring in the radial directiondisengages from the sidewall face 7 of the ring groove because of axialrunout of the housing or shaft. This degrades sealing properties.

On the other hand, in a case where L is larger than 1.2 mm or ⅔ of thedimension (thickness) a1 of the seal ring in the radial direction, thewedge-like gap (that is formed between the side face of the seal ringand the sidewall face of the ring groove and opens inward in the radialdirection) is small. Thus, the generated canceling pressure is small andthe friction reducing effects are insufficient.

Moreover, in order to maintain the sealing properties even in a casewhere the ring groove 4 is formed in a manner where it broadens outwardbecause of variations in the processing accuracy of the sidewall face 7of the ring groove, a second inclined face 57 can be provided on theinner circumferential side of the flat column portion 54 providedbetween the concave portions distanced away from each other in thecircumferential direction. This second inclined face 57 is formedcontinuously to reach a region on the inner circumferential side of theconverging portion 52.

FIG. 3( b) shows a cross-sectional view of the column portion. Thelength M of the second inclined face 57 in the radial direction ispreferably in the range from ⅕ to ½ of the width (a1−L) from theinnermost point of the seal ring 5 to the outermost point of the firstinclined face 51 in the radial direction. The length M, set in the abovemanner, makes the innermost point in the radial direction of the flatportion of the side face of the seal ring closer to the outermost pointin the radial direction of the concave portion. This therefore makes anoil-pressure opening (corresponding to A in FIG. 1) in which inner oilpressure is released to the outside is reduced. Thus, it is possible tomaintain excellent sealing properties.

In a case where the length M, in the radial direction of the secondinclined face 57 in the inner circumferential part of the column portion54, is less than ⅕ of (a1−L), the oil-pressure opening cannot be madesufficiently small. Therefore the sealing properties cannot besignificantly improved, if the wall face of the ring groove is inclinedin such a manner that the groove wall broadens outward. In a case wherethe length M in the radial direction is larger than ½ of (a1−L), thecharacteristics provided by the shape of the column portion 54 cannot beachieved.

The inclination angle β is preferably in the range from 8° to 60°, andmore preferably around 45°. In a case where the inclination angle β issmaller than 8°, the abutting end portion 50 is also inclined andtherefore the sealing properties may be degraded. On the other hand, ina case where the inclination angle β is larger than 60°, a gap may begenerated between the concave portion in the side face of the seal ringand the wall of the ring groove when the inner circumferential face ofthe seal ring comes into contact with the wall of the ring groove. Inthis case, an oil leakage path may be generated, thereby losing thesealing function.

The number of concave portions is preferably in the range from 4 to 16.In a case where the number of concave portions is less than 4, i.e., 1,2 or 3, the smoothly transfer of oil entering the concave portion into asliding face as the column portion 54 is reduced, and thus anyimprovement of abrasion resistance is minimal. In addition, a liftingforce is also small because its direction becomes closer to a directionperpendicular to the rotating direction of the seal ring due to theconical inclined face 52. Therefore, dragging torque is not markedlyreduced.

On the other hand, in a case where the number of concave portions ismore than 16, the wedge-like gap in the circumferential direction whichis formed between the sidewall face 7 of the ring groove and the concaveportion of the seal ring 5 becomes small and the number of columnportions 54 increases. This increases the contact area between the ringgroove and the seal ring. Thus, any significant reduction in torque lossarising from between the side face of the seal ring and the wall of thering groove is not achieved. Experiments showed this fact. In a casewhere the number of concave portions is in the range from 8 to 12,significant reductions in friction are achieved.

In the above description, the term “canceling pressure” means a pressurereducing a pushing pressure applied to the opposite side face by oilpressure.

In the drawings, a structure is shown in which the structure of thepressure-receiving side face, and that of the contact side face whichcomes into contact with the wall face of the ring groove, aresymmetrical. However, in a case where only the contact side face isformed to include the concave and column portions of the presentinvention, the advantageous effects of the present invention can also beachieved. From the viewpoint of workability when the seal ring ismounted in the ring groove, it is preferable that the seal ring have astructure in which both side faces are symmetrical and have nodirectionality.

EXAMPLE

An example of the present invention is now described. A main feature ofthe seal ring of the present invention is that low oil leakage and lowfriction are achieved irrespective of the processing accuracy of thesidewall face 7 of the ring groove. Thus, in this example, a shafthaving a ring groove that had a sidewall face 7 with an inclinationangle of 1.5°, and broadened outward was used (see FIG. 9). The shaft 1and the housing 2 were made of steel. The width and the depth of thering groove were 0.3 mm and 0.17 mm, respectively.

The seal ring 5 was made of polyether-ether-ketone (PEEK) resin withcarbon fibers added thereto. In the seal ring 5, an outer (nominal)diameter was Φ50, the width in the axial direction was 2.35 mm, thethickness in the radial direction was 2.0 mm, and the inclination angle(α) of the deepest inclined portion of the concave portion of the sideface was 16±2°. Moreover, the width of the portion between the outermostpoint of the deepest inclined portion and the outer circumferential faceof the seal ring in the radial direction was 1.0 mm (corresponding to ½of the thickness a1 in the radial direction). The inclination angle (β)of the second inclined face was 45±2°. Furthermore, fourteen concaveportions (a single concave portion was formed by one deepest inclinedportion and converging portions on both sides of the deepest inclinedportion) were formed, while fifteen second inclined faces 57 (one secondinclined face 57 was arranged on each side of the abutting endstructure) were also formed. The width of each of the deepest inclinedportions in the circumferential direction was 20 times the width of thesecond inclined face in the circumferential direction. The width of theconverging portion in the circumferential direction (each side) was 1/10of the width of a deepest inclined portion in the circumferentialdirection.

In addition, in a comparison to example, a conventional seal ring havinga groove extending in the circumferential direction on its side face(comparative example 1), and a one-tier tapered seal ring in which itsside face had a uniform inclination angle (comparative example 2) wereformed from the same material to have equivalent respective dimensionsas those in the example. The inclination angle of the side face of theone-tier tapered ring was 5±1°.

While the above seal rings were mounted in the aforementioned groove onthe shaft, oil leakage and friction were tested under a condition inwhich a rotating speed of the housing was 3,000 rpm, oil pressure was1.27 Mpa, and the oil temperature was 120° C. FIG. 10 shows the testresults.

From FIG. 10, it was confirmed that friction in the case of using theseal ring of the example according to the present invention was lowerthan that when using the seal ring of the comparative example 1. It wasalso lower than the one-tier tapered seal ring of the comparativeexample 2. Moreover, the amount of oil leakage in the seal ring of thepresent invention was ½ or less of that of the seal rings of thecomparative examples. Thus, it was found that excellent sealingproperties could be achieved by providing an inclination on the innercircumferential side of the flat column portion of the side face,irrespective of the processing accuracy of the sidewall face of the ringwall.

In addition, the seal rings having no concave portion (comparativeexample 3: the seal ring having a rectangular cross section), fourconcave portions, eight concave portions and sixteen concave portions onthe side faces, respectively, were manufactured.

While each of those seal rings was mounted in the aforementioned ringgroove of the shaft, oil leakage and friction were tested under acondition in which a rotating speed of the housing was 2,000 rpm, oilpressure was 1.5 Mpa, and the oil temperature was 120° C. FIG. 12 showsthe test results.

From FIG. 12, it was found that the seal ring of the present inventionwhich had concave portions in its side face could reduce friction, ascompared with comparative example 3. The relationship between the numberof the concave portions and friction was a downward convex curve. Whenthe number of the concave portions was 4 and 16, friction was reduced to⅔ of that in the comparative example 3. In addition, when the number ofthe concave portions was in the range from 8 to 12, the furtherreduction of friction was confirmed.

On the other hand, the oil leakage amount of the seal ring of thepresent invention having concave portions did not depend on the numberof the concave portions. In all examples, the oil leakage amount was ½or less of that of the one-tier tapered seal ring of comparative example2. From the aforementioned facts, it was found that the seal ring of thepresent invention could provide excellent sealing properties even if thering groove broadened outward.

The seal ring according to the present invention can achieve lowfriction and low oil leakage that are optimum, irrespective of theprocessing accuracy of the wall face of a ring groove on a shaft.

Thus, by using this seal ring it is possible to improve the fuelconsumption associated with the use of a product incorporating a sealring.

1. A seal ring to be mounted in a ring groove provided on an outercircumferential surface of a shaft, the seal ring comprising an outercircumferential face, an inner circumferential face, andpressure-relieving side and contact side faces between said outercircumferential face and said inner circumferential face; said seal ringdimensioned and configured to receive pressure from oil supplied to thering groove at its pressure-receiving side face and its innercircumferential face to achieve sealing by its contact side face whichis opposite to the pressure-receiving side face and comes into contactwith a wall face of the ring groove and its outer circumferential face,wherein a plurality of circumferentially extending concaves are providedalong an inner circumferential part of the contact side face andseparated from each other along the circumference of the side face bycolumnar surfaces, each end of each of said plurality ofcircumferentially extending concaves converges with a surface of theside face to form a converging point, adjacent converging points beingseparated from each other by said columnar surface, each of saidcolumnar surfaces extends radially outwardly from a line extendingbetween adjacent converging points to an outer circumferential edge ofthe side face, each of the concaves is formed by a first deepestinclined face provided in the inner circumferential part of the sideface of the seal ring, the first deepest inclined face being provided toreduce a thickness of the seal ring toward an inner circumference of theseal ring, and a second inclined face is provided on an innercircumferential side of each columnar surface and extends radiallyinwardly from said line extending between adjacent converging points tothe inner circumferential edge of the side face of the seal ring toreduce the thickness of the seal ring toward the inner circumference ofthe seal ring, said first deepest inclined face and second inclined faceextending continuously from the contact side face to the innercircumferential face.
 2. The seal ring according to claim 1, wherein aninclination angle measured with respect to a plane perpendicular to theaxial center of the seal ring of the first deepest inclined face is inthe range from 8° to 45°, and a dimension (L) between an outermost pointof the first deepest inclined face in the radial direction and the outercircumferential face of the seal ring is 0.4 mm or larger and is equalto or smaller than ⅔ of the thickness (a1) of the seal ring in theradial direction.
 3. The seal ring according to claim 2, wherein aninclination angle measured with respect to a plane perpendicular to theaxial center of the seal ring of the second inclined face is in therange from 8° to 60°, and a dimension (M) of the second inclined face inthe radial direction is in the range from ⅕ to ½ of a dimension (a1−L)from the inner circumference of the seal ring to an outermost point ofthe first deepest inclined face in the radial direction.
 4. The sealring according to claim 3, wherein a width of the first deepest inclinedface in the circumferential direction is 8 to 50 times as large as awidth of the second inclined face in the circumferential direction, anda number of the concaves included in said contact side face of the sealring is in the range from 4 to
 16. 5. The seal ring according to claim2, wherein a width of the first deepest inclined face in thecircumferential direction is 8 to 50 times as large as a width of thesecond inclined face in the circumferential direction, and a number ofthe concaves included in said contact side face of the seal ring is inthe range from 4 to
 16. 6. The seal ring according to claim 1, whereinan inclination angle measured with respect to a plane perpendicular tothe axial center of the seal ring of the second inclined portion is inthe range from 8° to 60°, and a dimension (M) of the second inclinedface in the radial direction is in the range from ⅕ to ½ of a dimension(a1−L) from the inner circumference of the seal ring to an outermostpoint of the first deepest inclined face in the radial direction, wherea1 is the thickness of the seal ring in the radial direction and L is adimension between an. outermost point of the first deepest inclined facein the radial direction and the outer circumferential face of the sealring.
 7. The seal ring according to claim 6, wherein a width of thefirst deepest inclined face in the circumferential direction is 8 to 50times as large as a width of the second inclined face in thecircumferential direction, and a number of the concaves included in saidcontact side face of the seal ring is in the range from 4 to
 16. 8. Theseal ring according to claim 1, wherein a width of the first deepestinclined face in the circumferential direction is 8 to 50 times as largeas a width of the second inclined face in the circumferential direction,and a number of the concaves included in said contact side face of theseal ring is in the range from 4 to 16.